In international relations, a concession is a "synallagmatic act by which a State transfers the exercise of rights or functions proper to itself to a foreign private person which, in turn, participates in the performance of public functions and thus gains a privileged position vis-a-vis other private law subjects within the jurisdiction of the State concerned."[1] International concessions are not defined in international law and do not generally fall under it. Rather, they are governed by the municipal law of the conceding state. There may, however, be a law of succession for such concessions, whereby the concession is continued even when the conceding state ceases to exist.[1]

In international law, a lease is "an arrangement whereby territory is leased or pledged by the owner-State to another State. In such cases, sovereignty is, for the term of the lease, transferred to the lessee State."[2] The term "international lease" is sometimes also used to describe any leasing of property by one state to another or to a foreign national, but the normal leasing of property, as in diplomatic premises, is governed by municipal, not international, law. Sometimes the term "quasi-international lease" is used for leases between states when less than full sovereignty over a territory is involved. A true international lease, or "political" lease, involves the transfer of sovereignty for a specified period of time. Although they may have the same character as cessions, the terminability of such leases is now fully accepted.[2]

The term "concession" may be used as a synonym for "leased territory", especially with respect to the concessions in China.
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The Guatemalan parliament issued a decree on 4 May 1843 by virtue of which the district of Santo Tomas was given "in perpetuity" to the Compagnie belge de colonisation, a private Belgian company under the protection of King Leopold I. Belgian colonizing efforts ceased after a few years, due to the lack of financial means and the harsh climate.

On 20 November 1846, a British concession in Shanghai (in China) was established (after the 16 June 1842 – 29 August 1842 British occupation of Shanghai, since 17 November 1843 a Treaty Port); on 27 November 1848, this concession was expanded, but on 21 September 1863 (after the 1862 proposal to make Shanghai an independent "free city" was rejected) an International Settlement in Shanghai was created by union of the American and British concessions (consummated in December 1863).

The British concession in Tianjin (Tientsin), in which the trade centred, was situated on the right bank of the river Peiho below the native city, occupying some 200 acres (0.81 km2). It was held on a lease in perpetuity granted by the Chinese government to the British Crown, which sublet plots to private owners in the same way as at Hankou (Hankow). The local management was entrusted to a municipal council organized on lines similar to those at Shanghai.[4]

Following the First World War the Republic of France granted Canada perpetual use of a portion of land on Vimy Ridge under the understanding that the Canadians were to use the land to establish a battlefield park and memorial. The park, known as the Canadian National Vimy Memorial, contains an impressive monument to the fallen, a museum and extensive recreations of the wartime trench system, preserved underground tunnels and cemeteries.

Between 1882 and 1884, the Qing Empire obtained concessions in Korea at Incheon, Busan and Wonsan. The concessions were occupied by Japan in 1894 after the outbreak of the First Sino-Japanese War. After China's defeat in that war, Korea (now with Japanese support) declared the unequal treaties with Qing China to be void, and unilaterally withdrew the extraterritoriality and other powers granted to China in respect of the concessions. The concessions were formally abolished in 1898.

6 April 1849 French concession in Shanghai (since 17 November 1843 a Treaty Port) established; 17 July 1854 Municipal Council established. Relinquished by Vichy France to a Japan-sponsored puppet government in China, formally returned to China by France in 1946.

Macau: around 1552–1553, the Portuguese obtained permission to establish a settlement as a reward for defeating pirates and to mediate in trade between China and Japan and between both nations and Europe; it was leased from the empire of China from 1670. The concession turned into a Portuguese colony in mid-19th Century. The Chinese government assumed sovereignty over Macau on 20 December 1999, ending 329 years of Portuguese colonial rule.

Hanko (Hangö in Swedish), a peninsula near the Finnish capital Helsinki, was leased for a period of 30 years by the Soviet Union from its northwestern neighbour—and former possession in personal union—Finland for use as a naval base in the Baltic Sea, near the entry of the Gulf of Finland, under the Moscow Peace Treaty that ended the Winter War on 6 March 1940; during the Continuation War, Soviet troops were forced to evacuate Hanko in early December 1941, and the USSR formally renounced the lease—early given the original term until 1970—in the Paris peace treaty of 1947. The role of the Hanko naval base was replaced by Porkkala, another Finnish peninsula, a bit farther east at the Gulf of Finland, in the armistice between Finland and the Soviet Union of 19 September 1944; it was returned to Finland in January 1956. In both cases, the Soviets limited themselves to a military command, without any civilian administration.

Khmeimim Air Base in Syria is leased to the Russian government for a period of 49 years, with the Russian government having extraterritorial jurisdiction over the air base and its personnel.[5][6]

Guantanamo Bay: leased from Cuba (which now disputes the lease) under 1903 and 1934 treaties in perpetuity; no civilian administration, only military command.

Two in imperial China:

1848/54 American concession in Shanghai (since 17 November 1843 a Treaty Port) established, until on 21 September 1863 (after the 1862 Proposal to make Shanghai an independent "free city" was rejected) an International Settlement in Shanghai was created by union of the American and British concessions (consummated December 1863).

21 September 1863 (after the 1862 Proposal to make Shanghai an independent "free city" was rejected) an International Settlement in Shanghai was created by union of the American and British concessions (consummated December 1863); in 1896 the concession was expanded.

On 7 July 1927, a Chinese city government of Greater Shanghai was formally established.
In January/February 1931, the Japanese occupied the Hongkou District (Hongkew), and on 9 November 1937 the Chinese city of Shanghai, but only on 8 December 1941 would Japanese troops occupy the International Settlement (but not the French concession); it was dissolved by Japan in 1942.
In February 1943 the settlement is officially abolished by the U.S. and Britain; in September 1945, the last territory is restored to China.